The Weather Makers: How Man is Changing the Climate and What it Means for Life on Earth by Tim Flannery (Atlantic Monthly Press, 352 pages, $24, March, 2006)

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That sentence, which opens one of the final chapters of The Weather Makers, a new book by renowned Australian scientist and explorer Tim Flannery, illustrates the remarkably rapid transformation of the scientific debate over the causes and consequences of global warming in recent years. (Note added 2/12/07: Flannery was named Australian of the Year 2007 in a ceremony on the lawns of the Parliament House, with the Prime Minister presenting the award. The Weather Makers won the 2006 New South Wales Premier's Book of the Year Award. Details at this link.)

A decade ago, some climate-change contrarians were still disputing the existence of the phenomenon. By the late 1990s, as data accumulated about Earth's rising average temperature, they shifted the target of their doubting to the role of human activity. Soon after the turn of the new century, climate modeling and further research rendered that position untenable as well.

Today, scientific discussion begins with the acceptance of both global warming and its anthropic cause, primarily the burning of fossil fuels. The major questions now concern how much and how fast warming will occur, what changes in climate will result, and what consequences that will have for the environment and ecology.

Answering those questions requires certain assumptions about people's behavior and thus yields a variety of climate-change scenarios. Since individuals can change their behavior and nations can change their policies in response to available information, science, politics, and culture are unavoidably intertwined in the analysis.

Thus Flannery and journalist Elizabeth Kolbert of New Yorker magazine, whose Field Notes From a Catastrophe is appearing in bookstores at the same time as The Weather Makers, consider not only the natural sciences, but also the social sciences in their discussions of climate change.

The two books describe the same facts and include many of the same geographical settings and events. They sound similar warnings about the danger of continued inaction and political foot dragging. They speak about the possibility of abrupt climate changes with the potential to disrupt both economies and ecologies.

They discuss the extinction of many species and of the loss of vulnerable human cultural groups, such as the Inuit who depend on animals destined for extinction as the Arctic sea ice disappears, and the small nations of the Pacific whose protective coral reefs will die out and whose atolls will be swamped by rising sea levels.

Both books even describe plausible but unlikely scenarios for the late 21st century, such as the Gulf Stream shutting down and plunging Europe into an ice-age climate. A more likely worst-case set of circumstances would include widespread crop failure and loss of water resources, an upsurge in extreme weather events such as floods, hurricanes, and heat-waves, and an increase in tropical disease. The results would be mass migrations and the possibility of conflicts that threaten civilization as we know it.

Both authors presume that people will be smart enough to act before such catastrophes loom, but they also point out that even with prompt action, the world is already committed to major climate change in this century. That will result from two kinds of inertia: the time for the climate to respond to carbon dioxide and other greenhouse gases already in the atmosphere; and the time it takes to make social, economic, and technological changes necessary to decrease the rate that humans produce those gases.

Despite these similarities, the books are very different in tone and detail. Kolbert's style is journalistic and her approach is reminiscent of Rachel Carson, presenting an overview of the scientific analysis in the context of broad human stories and historical trends. Her journalistic training gives her an advantage over Flannery in discussing the current political questions and the way the world has been responding to them. Her skillful presentation leads readers inexorably toward this concluding challenge worthy of Silent Spring:

"As the effects of global warming become more and more disruptive, will we react by finally fashioning a global response? Or will we retreat into ever narrower and more destructive forms of self-interest? It may seem impossible to imagine that a technologically advanced society could choose, in essence, to destroy itself, but that is what we are now in the process of doing."

Flannery's approach is more like Carl Sagan's. He provides deeper insight into climate modeling than Kolbert plus considerable technological detail about possible engineering solutions. He also deliberately picks a political fight with the contrarians, whom he views as obstacles to saving the planet, in a chapter entitled "People in Greenhouses Shouldn't Tell Lies."

His style is clear and enthusiastic about the science even when its predictions are frightening. Some of his conclusions go beyond the current scientific consensus, though they are indeed plausible and well reasoned.

Of particular note is his discussion of "Time's Gateways," which mark abrupt, irreversible transitions in global or regional climate. He makes a plausible case that a "magic gate" opened in the western tropical Pacific Ocean in 1976. Before that year, the region's surface temperature frequently dropped below 67 degrees Fahrenheit. Since then, it has rarely been below 77. Another gateway came in 1998, which seems to mark a dramatic change in the El Nino-La Nina cycle. Both of these changes have resulted in dramatic shifts in rainfall patterns, including extended droughts in the African Sahel, Australia, and southeast Asia.

Arguably, those events may be no more than transitory fluctuations. But they may instead be harbingers of more serious transitions to come as the world's climate passes through other gateways later in this century. If they are the latter, the contrarian strategy of waiting for more data before acting is risky business indeed.

Flannery's similarity to Sagan runs deep, including his willingness to discuss unlikely but plausible catastrophes. Nearly ten years after Sagan's death, people still question the wisdom of his public pronouncements and magazine articles about a scientific paper on the effects of a massive nuclear exchange between the United States and the Soviet Union, for which he was the last-listed but most vocal of five authors.

Sagan used his popularity to draw attention to the "nuclear winter" scenario, which described a situation like the global chill that followed the impact of the killer asteroid that ended the reign of the dinosaurs. That may not have been a likely consequence of an all-out nuclear war, but it was plausible. Its dire consequences commanded the world's attention, and it probably influenced discussions that led to nuclear weapons treaties.

Is Flannery wise to devote so much attention to his estimated five percent chance of the failure of the Gulf Stream before the end of this century? Will that approach also bring badly needed attention to the more likely, less serious but still concerning climate scenarios? Or will it provoke attacks from critics that this book is the work of a left-wing ideologue and harm its credibility?

As a middle-of-the-political-road scientist who thinks policy-makers should consider Flannery's views quite seriously, I hope for the former but am afraid it will be the latter, largely because of two other aspects of the book. First, Flannery chooses to use the language of the Gaia hypothesis to discuss the intricate interconnections of Earth's atmosphere, land, and oceans. That will give many readers an uncomfortable sense that the book belongs on the "New Age" shelf.

Second, he makes an argument that the present tragedy in the Darfur region of Sudan is the result of a climate-change induced competition for resources rather than genocide. He may be right, but including that small, nearly irrelevant point will have an unfortunate side effect: It will open the door for contrarian critics to suggest that the author has a hidden agenda.

Physicist Fred Bortz has written books for young readers about weather and planetary science. He blogs about global warming and other "hot" scientific topics at www.scienceblog.com/cms/blog/fred_bortz.